DESCRIPTION: (Applicant's Abstract) The purpose of this study is to map and analyze the networks of Injection Drug Users (IDUs) constructed from the needle exchange data. The IDU needle networks are then to be used to (1) investigate how network properties co-vary with demographic, drug use and HIV risk-related behavior; (2) determine the stability and dynamic of IDU networks with attention to the influence of the needle exchange itself; (3) simulate HIV transmission dynamics based on network measures within the same study. The matching of barcoded needles to individuals who receive and return needle exchange needles permits the construction of a needle transaction and interchange network that is the primary data source for the proposed investigation. Our major purpose is to demonstrate how needle exchange data may be used to construct IDU networks and to use these network constructs/variables to understand IDU behavior. These "needle networks" represent needle transaction processes such as selling, trading, swapping, lending/borrowing, finding and perhaps sharing or needles. Although, it is important to determine the theoretical, methodological and computer programming aspects of needle networks, this proposal also addresses how needle networks are influenced and influence drug use and HIV-risk behavior.